The present invention relates to phase change ink compatible colorants, to the use of these phase change ink compatible colorants in phase change inks, and to phase change inks produced therefrom which are employed in phase change ink jet printing devices.
In general, phase change inks are in the solid phase at ambient temperature, but exist in liquid phase at the elevated operating temperature of an ink jet printing device. At the liquid phase ink jet operating temperature, droplets of liquid ink are ejected from the printing device and, when the ink droplets contact the surface of a wide variety of printing media, they quickly solidify to form a predetermined pattern of solidified ink drops.
Phase change ink is desirable since it remains in a solid phase at room temperature, during shipping, long-term storage, etc. Also, the problems associated with nozzle clogging due to ink evaporation are largely eliminated, thereby improving the reliability of ink jet printing. Furthermore, since the ink droplets solidify immediately upon contact with the substrate, migration of ink along the printing medium is prevented and dot quality is improved.
The initial prior art on phase change inks for ink jet printing involved monochrome inks jetted by electrostatic printing devices. Thus, for example in U.S. Pat. No. 3,653,932, a low melting ink (30.degree. C. to 50.degree. C.) is provided employing an ink base comprising di-esters of sebacic acid. In a similar process, U.S. Pat. No. 3,715,219 describes another low melting point ink (30.degree. C. to 60.degree. C.) comprising a paraffin alcohol-based ink. However, when low melting point phase change inks are employed in printing onto a substrate, they exhibit offset problems, namely, when the printed substrates formed from these inks are stacked and stored for subsequent use, they can become adhered to one another, particularly if high ambient temperatures are experienced.
U.S. Pat. No. 4,390,369 and U.S. Pat. No. 4,484,948 describe methods for producing monochrome phase change inks which employ a natural wax ink base, such as Japan wax, candelilla wax, carnauba wax, etc., which is printed from a drop-on-demand ink jet device at a temperature ranging between 65.degree. C. and 75.degree. C. In U.S. Pat. No. 4,659,383, a monochrome ink composition is provided having an ink base comprising a C20-24 acid or alcohol, a ketone, and an acrylic resin plasticizer. These monochrome ink compositions are not durable and when printed can be smudged with routine handling and folding.
In Japanese patent application 128,053/78, amides which are solid at room temperature, such as acetamide, are employed as printing inks. U.S. Pat. No. 4,684,956 is directed to monochrome phase change inks utilizing synthetic microcrystalline wax (hydrocarbon wax) and microcrystalline polyethylene wax. This molten composition can be applied to a variety of porous and non-porous substrates using drop-on-demand ink jet application techniques.
EP 0187352 and EP 0206286 reference phase change ink jet printing in color. The ink bases for these systems comprise fatty acids, a thermoplastic polyethylene and a phase change material in the first application; and the alcohol portion of a thermal setting resin pair, a mixture of organic solvents (o- and p-toluene sulfonamide) and a dye in the second application.
Jet printing colored inks onto a light transmissive medium for displaying color images by overhead projection has historically been a problem. For example, in the case of aqueous inks, special coatings must be provided on the light transmissive medium in order to absorb the aqueous phase so that images of high quality are formed. See, for example, U.S. Pat. No. 4,503,111, U.S. Pat. No. 4,547,405 and U.S. Pat. No. 4,555,437. Even though special coatings are not required on receptor films used for phase change ink jet printing, when prior art color phase change inks are applied in a thin film of substantially uniform thickness to a light transmissive receiver sheet, they are not rectilinearly light transmissive. It is this rectilinearly light transmissive property which creates intense, saturated colors.
In U.S. Pat. No. 4,830,671, a hot-melt or phase change color ink composition is provided having the properties of stability and uniformity of performance under ink jet printing conditions. The resinous binder for the above-described phase change ink is the condensation reaction product of one equivalent of polmerized fatty acid, two equivalents of diamine and two equivalents of a monocarboxylic acid.
A phase change ink composition is described in U.S. Pat. No. 4,889,560, and in U.S. Pat. No. 4,992,304, and in U.S. Ser. No. 07/389,222, all of which are assigned to the assignee of this patent application. U.S. Pat. No. 4,889,560 and U.S. Pat. No. 4,992,304 are incorporated herein by reference. The carrier composition is preferably a fatty amide-containing compound. The thin films of a substantially uniform thickness of this ink composition are also rectilinearly light transmissive.
The phase change ink carrier composition forms an ink by combination with a phase change ink compatible colorant. Preferably, a colored phase change ink will be formed by combining the above-described ink carrier composition with compatible subtractive primary colorants. The subtractive primary colored phase change inks of this invention comprise four component dyes, namely, cyan, magenta, yellow and black. The subtractive primary colorants employed typically comprise dyes from either class of Color Index (C.I.) Solvent Dyes and Disperse Dyes, and a limited number of Basic Dyes.
Many dyes having ionic functional groups, as for example, Acid Dyes and Direct Dyes, are soluble in aqueous ink systems, and exhibit visually desirable colors. However, these dyes have been found to be minimally soluble in non-polar, non-aqueous phase change ink systems.